[CI] Remove legacy frontend tests

The frontend tests have been moved to their own repository to reduce the
size of the main TVM repository and make CI more efficient. This commit
removes all frontend-related test files and updates the CI scripts
accordingly.

Key changes:
- Remove all frontend test files from tests/python/frontend/
- Update task_python_frontend.sh script
- Update conftest.py to remove frontend-specific test configurations

conftest.py

@@ -31,23 +31,17 @@
 # taken from the 20 (arbitrary number) of tests as from
 # https://ci.tlcpack.ai/job/tvm/job/main/2907/testReport
 _slowest_tests = [
-    "tests/python/frontend/tensorflow/test_forward.py::test_forward_broadcast_args",
-    "tests/python/frontend/tensorflow/test_forward.py::test_forward_broadcast_to",
     "tests/python/topi/python/test_topi_conv2d_int8.py::test_conv2d_nchw[int8]",
     "tests/python/topi/python/test_topi_conv2d_int8.py::test_conv2d_nchw[uint8]",
     "tests/python/topi/python/test_topi_upsampling.py::test_upsampling3d",
     "tests/python/topi/python/test_topi_upsampling.py::test_upsampling3d",
     "tests/python/topi/python/test_topi_conv2d_int8.py::test_conv2d_nchw[int8]",
-    "tests/python/frontend/tflite/test_forward.py::test_all_elemwise",
-    "tests/python/frontend/pytorch/test_object_detection.py::test_detection_models",
     "tests/python/topi/python/test_topi_conv2d_int8.py::test_conv2d_nchw[uint8]",
     "tests/python/topi/python/test_topi_conv2d_NCHWc.py::test_conv2d_NCHWc",
     "tests/python/topi/python/test_topi_conv2d_hwnc_tensorcore.py::test_conv2d_hwnc_tensorcore",
     "tests/python/contrib/test_tensorrt.py::test_binary[compile]",
-    "tests/python/frontend/pytorch/test_forward.py::test_segmentation_models",
     "tests/python/topi/python/test_topi_conv2d_NCHWc.py::test_conv2d_NCHWc",
     "tests/python/relay/test_py_converter.py::test_global_recursion",
-    "tests/python/frontend/tensorflow/test_forward.py::test_forward_ptb",
     "tests/python/relay/test_op_level6.py::test_topk",
     "tests/python/topi/python/test_topi_conv2d_winograd.py::test_conv2d_nchw",
     "tests/python/relay/test_py_converter.py::test_global_recursion",